Titanium filament for use in vacuum techniques

ABSTRACT

Filaments for vacuum devices of the titanium getter type, said filaments comprising a refractory core of tungsten, molybdenum or tantalum which is coated with a layer of pure titanium.

0 United States Patent 1191 1111 3,724,049 Biguenet 1 Apr. 3, 1973 [54] TITANIUM FILAMENT FOR USE IN [58] Field of Search ..29/198, 191

VACUUM TECHNIQUES [75] Inventor: Charles Biguenet, Paris, France [56] References C'ted [73] Assignee: CSF-Compagnie Generale de Teleg- UNITED STATES PATENTS raphies Sans FiL ri France 2,491,284 12 1949 Sears ..29/198 2,847,331 8/1958 Ashley... ..29/198 [22] Flled' 1971 2,975,075 3/1961 Beese ..29/198 21 Appl 112 54 3,071,491 1/1963 Horn ..29/198 Related US. Application Data Primary Examiner-J-lyland Bizot [63] Continuation-impart of Ser. No. 722,654, April 19, Ammey cushma" Darby Cushma 1968, abandoned. ABSTRACT [30] Foreign Application Priority Data Filaments for vacuum devices of the titanium getter type, said filaments comprising a refractory core of ApLZl, France g te molybdenum or tantalum is coated 'th 1 f t't 52 US. (:1 ..29/191, 29/198 M a aye) pure amum [51] Int. Cl. ..B32b 15/00 1 Claim, 3 Drawing Figures PmmFnmm 1913 v 3,724,049

' INVENTOR CHnnles Bmueurr ATTORNEYS TITANIUM FILAMENT FOR USE IN VACUUM TECHNIQUES This application is a continuation-in-part of my copending application Ser. No. 722,654, filed Apr. 19, 1968 now abandoned.

The present invention relates generally to improved filaments for vacuum devices of the titanium getter type. By employing the improved filament of the present invention, lower pressures can be obtained in less time than could be obtained with devices employing filaments of the prior art.

The ability of titanium to attract and absorb residual gas molecules in a vacuum makes this substance a very valuable material in vacuum techniques where it is used in various ways, including a getter in a vacuum device of the getter type.

In all cases where titanium is used as the getter in a vacuum device, the purity of the titanium is of paramount importance. Generally speaking, the ultimate pressure obtainable with a vacuum pump of the getter type is dependent on the equilibrium between the evacuation by the pump and the degasing by the getter of the different parts forming the envelope being evacuated. If, therefore, the getter material itself releases gases, as a result of certain surface impurities or gases trapped within it, during the operation of the vacuum device, the ultimate vacuum obtainable would be proportional to the desorption of gases by the getter material.

A systematic analysis by mass spectrometry of residual gases in vacuum containers, which had been evacuated with a getter type vacuum pump using a titanium getter, showed the presence of large quantities of argon and hydrocarbons. It has been found that the presence of residual argon gas in vacuum produced by titanium getter pumps results from the metallurgical techniques used in producing the titanium metal, especially of the repeated heating of the titanium metal in furnaces under an argon atmosphere. The presence of residual hydrocarbons in vacuum produced by titanium pumps has been found to be due to drawing lubricants used in the production of the titanium wire used for the filament of the getter pump.

The titanium getter material of a getter vacuum pump is heated to an operating temperature which ranges from about 800 C to about l,600 C. Conventionally, electrical resistance heating filaments or wires are used to heat the titanium getter. A commonly used construction is a core of a refractory or high melting point material, for example, a core made of a high melting point metal such as tungsten or molybdenum on which a titanium wire is wound in spiral fashion. The spiral titanium wire is the getter. The titanium wire is normally contaminated with impurities mentioned hereinbefore and the vacuum getter pump utilizing the contaminated element will be capable of producing only a limited vacuum, as explained hereinbefore.

Depositing a layer of'chemically pure titanium by pyrolysis on a titanium core, i.e., a core of titanium produced by metallurgical techniques, has been suggested as a way of avoiding the problem caused by the contaminated titanium produced by metallurgical techniques; however, such a filament has proved to be unsuitable for titanium vacuum getter pumps, because the sublimation of the contaminants from the core material rapidly affects the whole of the structure again leading to the above-mentioned drawbacks.

It is an object of the present invention to provide a composite filament for titanium getter pumps in which a layer of chemically pure titanium is coated upon a core member which does not contaminate the chemically pure titanium coating. The titanium getter filament of the present invention, therefore, does not have the drawbacks associated with the titanium getters 'of the prior art, as mentioned hereinbefore. Another object of the present invention is toprovide a composite titanium getter filament in which the core material is used as an electrical resistance heater for the titanium coating thereon.

It has now been found that an improved filament for a titanium getter pump can be provided comprising a support core of a material selected from tungsten, molybdenum and tantalum coated with a layer of chemically pure titanium. The tungsten, molybdenum or tantalum core can be connected to a source of electrical current which heats the core and titanium coating to its operating temperature. The core of tungsten, molybdenum or tantalum does not undergo any appreciable sublimation and, therefore, does not contaminate the pure coating of titanium which surrounds the core.

The improved filaments of the present invention can be formed from an extended core such as a rod. The core or rod is made of tungsten, molybdenum or tantalum and is coated with chemically pure titanium. Alternatively, the core can be wound with a wire of tantalum, molybdenum or tungsten in spiral fashion. The core and the helically wound wire thereonare coated with the chemically pure titanium. The helical wire is used to improve support of the titanium coating.

The invention will be further understood by the following description with reference to the drawings in which:

FIG. 1 shows one preferred embodiment of a filament according to the present invention;

FIG. 2 shows diagrammatically a titanium pump using a filament according to the invention, and

FIG. 3 shows another preferred embodiment of a filament according to the invention.

Referring now to FIG. 1, one preferred construction of a filament according to the invention is shown. The filament comprises a core 11, which is of tungsten, molybdenum or tantalum, on which is wound a wire 12 in a spiral fashion. Wire 12 is of molybdenum, tungsten or tantalum. A layer 13 of chemically pure titanium is deposited on the wire 11 and spiral wire 12, for example, by pyrolysis of a titanium compound such as titanium iodide. The wire spirals 12 serve only as support for the titanium coating. The heating of the filament is obtained by passing a current through wire 11. At the operating temperature, the tungsten, molybdenum or tantalum wires 11 and 12 do not undergo any appreciable sublimation.

FIG. 2 shows diagrammatically a vacuum pump of the getter type equipped with a titanium getter filament according to the present invention. It comprises a primary suction pump 21 with its stopcock 21', an ionic pump 22 and a titanium sublimator 23 surrounded by a wall 24, cooled by liquid nitrogen which circulates in the cooling spiral 25. The evacuation envelope is shown at 26.

In FIG. 3, a second embodiment of a titanium filament for use in a vacuum pump of the getter type is shown. It is similar to the embodiment shown in FIG. 1 except that the helically wound wire '12 shown in FIG. 1 is omitted from the embodiment shown in FIG. 3. In FIG. 3, there is shown a central core or wire 31 which is made of tantalum, molybdenum or tungsten. Completely surrounding the wire 31 is a coating 33 of chemically pure titanium. The filament shown in FIG. 3 can be utilized in the vacuum pump of FIG. 2 in the form of a straight section, as shown, or it can be helically wound into a coil looking like a spring.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It should be understood, therefore, that the tungsten and tantalum, and having helically wound thereon a wire of a metal selected from the same group, said support member being coated with a layer of chemically pure titanium. 

